Lithium fluoride, and preparation method therefor and use thereof

Abstract

The present application provides lithium fluoride, and a preparation method therefor and a use thereof. The mass content of a carbonate in the lithium fluoride is less than or equal to 1000 mg / kg. The lithium fluoride has a D10 of less than or equal to 10 pm, a D50 of less than or equal to 20 pm, and a bulk density of 0.9-1.2 g / cm3.

Description

Lithium fluoride, its preparation method and application

[0001] This application claims priority to Chinese Patent Application No. 202411729269.3, filed on November 28, 2024, entitled "A lithium fluoride and its preparation method and application", the entire contents of which are incorporated herein by reference. Technical Field

[0002] This application relates to a lithium fluoride, and more particularly to a lithium fluoride, its preparation method and application, belonging to the field of lithium-ion batteries. Background Technology

[0003] Lithium fluoride, as an important lithium-based material, has a wide range of applications in many fields. With the increasing demand for lithium fluoride in traditional applications and the emergence of new applications such as optical fiber communication, high-energy chemical power sources, and aerospace, the research and preparation of lithium fluoride are attracting more and more attention.

[0004] Of particular importance is that lithium fluoride is an important raw material for electrolyte salts used in lithium-ion batteries, such as lithium hexafluorophosphate and lithium bis(fluorosulfonyl)imide. Its quality has a great impact on the quality of electrolyte products. Therefore, it is crucial to develop a lithium fluoride that is conducive to improving the quality of electrolyte salts. Summary of the Invention

[0005] This application provides a lithium fluoride having specific size specifications and low carbonate impurity content, which helps to prepare an electrolyte salt that can improve battery electrical performance.

[0006] This application provides a lithium fluoride, wherein the mass content of carbonate in the lithium fluoride is less than or equal to 1000 mg / kg;

[0007] The lithium fluoride has a D10 of less than or equal to 10 μm, a D50 of less than or equal to 20 μm, and a bulk density of 0.9-1.2 g / cm³. 3 .

[0008] The technical solution of this application was developed by the inventor based on the following discoveries:

[0009] The inventors, when preparing battery-grade products such as hexafluorophosphate or bis(fluorosulfonyl)imide using commercially available lithium fluoride as a raw material, found that impurity removal was difficult under conventional methods and operating times. Furthermore, when these products were applied to electrolytes, an increase in precipitates occurred. Analysis indicated that the precipitation was likely due to impurities carried by the hexafluorophosphate or bis(fluorosulfonyl)imide. Initially, it was assumed that these impurities were generated during the production process. Therefore, to reduce the impurity content, the synthesis process of hexafluorophosphate or bis(fluorosulfonyl)imide was improved. However, the improved process parameters did not significantly improve the problem. Further analysis of the raw materials revealed that some commercially available lithium fluoride products contain carbonate impurities, such as lithium carbonate. These carbonate impurities are likely inherent in the product's preparation using a carbonate-based raw material. It is precisely the use of raw materials containing carbonate impurities in the preparation of electrolyte products that leads to the difficulty in removing impurities and the increase in precipitates when applied to electrolytes. The inventors analyzed that the reason might be that lithium carbonate can also react with hydrofluoric acid, a raw material for the preparation of lithium hexafluorophosphate, and bisfluorosulfonylimide, a raw material for the preparation of lithium bisfluorosulfonylimide. Moreover, since carbonates are alkaline substances, they react with the raw materials more easily than lithium fluoride to produce water. Both lithium hexafluorophosphate and lithium bisfluorosulfonylimide are sensitive to water and will hydrolyze to produce impurities.

[0010] Due to production costs and other commercial considerations, the lithium fluoride used cannot avoid being prepared from carbonates, meaning that carbonates are inevitably present in lithium fluoride products. In this situation, the inventors could only try to solve the problem by reducing carbonate content, but found that simply reducing the carbonate content was insufficient given the inevitable presence of carbonates. Later, the inventors inadvertently discovered that only by simultaneously controlling both the carbonate content and the particle size of the lithium fluoride could the problems of difficult impurity removal and increased precipitates in the electrolyte when the product was used were solved. The reason is that when lithium fluoride products have large particle sizes and high alkaline content, when lithium fluoride participates in the reaction, substances on the surface of the lithium fluoride particles and lithium carbonate will react with other reactants. Since lithium carbonate is alkaline, it reacts preferentially with lithium fluoride, generating impurities. Furthermore, due to the large particle size of lithium fluoride, the reaction is not rapid, causing impurities to adhere to unreacted lithium fluoride. Further processed products will also adhere to these impurities, resulting in the final product containing both impurities and unreacted lithium fluoride. This leads to problems such as difficult-to-remove impurities and increased precipitation in electrolytes. Therefore, simply reducing the carbonate content without controlling the particle size will not prevent impurities from being trapped within the product. However, when the carbonate content is less than 1000 ppm, and the lithium fluoride has a D10 of less than or equal to 10 μm, a D50 of less than or equal to 20 μm, and a bulk density of 0.9-1.2 g / cm³, the desired product yields better results. 3At this time, due to the large presence of lithium fluoride and its small particle size, it will compete with carbonate for reaction and participate in the reaction quickly. The small lithium fluoride particles are quickly reacted, and the products and impurities will not form a coating relationship. Therefore, even if a small amount of impurities are generated in the end, they are easier to remove because the amount of impurities is very small and they exist independently in the system.

[0011] This application provides a method for preparing lithium fluoride, comprising the following steps:

[0012] 1) Mix lithium carbonate with water and pulp to form a lithium carbonate slurry with a mass percentage of 10-30%;

[0013] 2) Add hydrofluoric acid to the lithium carbonate slurry and react the system at a pH of 3-6 until the pH of the reaction system does not change, to obtain the reactant. Then, microwave dry the reactant to obtain the lithium fluoride.

[0014] The reaction temperature is 10-70℃; preferably, the reaction temperature is 30-60℃.

[0015] Currently, most commercially available lithium fluoride is produced by carbonizing lithium carbonate with carbon dioxide to obtain lithium bicarbonate, followed by fluorination of the lithium bicarbonate with hydrofluoric acid or ammonium fluoride to obtain lithium fluoride. However, this method suffers from problems such as high residual lithium carbonate content. Furthermore, the inventors discovered that when lithium fluoride products have large particle sizes and high lithium carbonate content, the lithium carbonate in the lithium fluoride, being alkaline, reacts preferentially with the lithium fluoride, generating impurities. Simultaneously, due to the large particle size of lithium fluoride, the reaction is not rapid, causing impurities to adhere to unreacted lithium fluoride. Further products will also adhere to these impurities, resulting in the final product containing both impurities and unreacted lithium fluoride. This leads to poor stability and precipitation problems in electrolyte salts prepared from lithium fluoride during storage and use. To optimize the purity of lithium fluoride, the preparation method of this application creatively involves pulping lithium carbonate and then reacting it with hydrogen fluoride to obtain crude lithium fluoride. Subsequently, microwave drying is used, which not only reduces the carbonate content in lithium fluoride but also adjusts the structural size of lithium fluoride. As a result, when preparing electrolyte salts using lithium fluoride as a raw material, the storage and application stability of the electrolyte salts can be significantly improved.

[0016] This application also provides a lithium fluoride prepared by any of the above-described methods, wherein the mass content of carbonate in the lithium fluoride is less than or equal to 1000 mg / kg.

[0017] The lithium fluoride has a D10 of less than or equal to 10 μm, a D50 of less than or equal to 20 μm, and a bulk density of 0.9-1.2 g / cm³. 3 .

[0018] This application provides lithium hexafluorophosphate and lithium difluorosulfonylimide, respectively, which are prepared by the above-mentioned lithium fluoride. Therefore, they have low impurity content, which helps to improve the electrical performance of the battery. Detailed Implementation

[0019] To make the objectives, technical solutions, and advantages of this application clearer, the technical solutions in the embodiments of this application will be clearly and completely described below in conjunction with the embodiments of this application. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art are within the scope of protection of this application.

[0020] Currently, when the inventors use commercially available lithium fluoride as a raw material to prepare battery-grade lithium salt products, such as hexafluorophosphate or difluorosulfonyl imide salt, according to conventional processes, they have found that the lithium salt products have a high impurity content, and the impurities are intermingled with the lithium salt products, making it difficult to achieve efficient impurity removal and resulting in a low lithium salt product recovery rate. Furthermore, when these lithium salt products are used in electrolytes, precipitation occurs during storage and application. Based on these findings, the inventors have made some optimizations to the lithium salt product preparation process, but with minimal improvement.

[0021] Therefore, the inventors attempted to improve the quality of commercially available lithium fluoride to enhance the performance of lithium salt products. During their research, they discovered that lithium fluoride contains carbonate impurities, such as lithium carbonate, which may be the primary cause of quality problems in lithium salt products. Specifically, carbonates, as alkaline compounds, are more likely to react with hydrogen fluoride (a raw material for lithium hexafluorophosphate) or bis(fluorosulfonyl)imide (a raw material for lithium bis(fluorosulfonyl)imide) to form water during the preparation of lithium salt products. Lithium hexafluorophosphate and lithium bis(fluorosulfonyl)imide have extremely poor water stability and readily react with water to generate other impurities that become trapped within them.

[0022] Currently, the technology for preparing lithium fluoride using lithium carbonate as a raw material is extremely mature, making it less feasible to prepare lithium fluoride by changing the raw material. Therefore, the inventors studied the control of carbonate content in lithium fluoride and achieved preliminary results. However, even after reducing the carbonate content, the quality of the lithium salt product still did not meet expectations.

[0023] Later, the inventors discovered that when the size specifications of lithium fluoride changed simultaneously, the quality of lithium salt products would also change.

[0024] Based on the above concept, this application provides a lithium fluoride, wherein the mass content of carbonate in the lithium fluoride is less than 1000 mg / kg; the lithium fluoride has a D10 of less than or equal to 10 μm, a D50 of less than or equal to 20 μm, and a bulk density of 0.9-1.2 g / cm³. 3 .

[0025] Using the lithium fluoride of this application as a raw material for preparing lithium salt products can significantly reduce the impurity content in lithium salt products, thereby improving the stability of the electrolyte and suppressing precipitation during storage and application. The inventors analyzed the reasons for this and believe that the size of the lithium fluoride also has a significant impact on the reaction process. Different sizes determine the degree of reaction between lithium fluoride, lithium carbonate, and hydrofluoric acid or lithium bis(fluorosulfonyl)imide. If the degree of reaction between lithium fluoride and hydrofluoric acid or lithium bis(fluorosulfonyl)imide is lower than that of carbonate, impurities will be generated in large quantities as the reaction proceeds, and the lithium fluoride cannot react quickly and completely. Ultimately, impurities and unreacted lithium fluoride will be trapped in the lithium salt product, leading to problems such as difficulty in removing impurities and poor electrolyte stability with easy precipitation. However, when the size of the lithium fluoride in this application meets the requirements of D10 ≤ 10 μm, D50 ≤ 20 μm, and a bulk density of 0.9-1.2 g / cm³, the results are satisfactory. 3 Furthermore, when the carbonate content is less than or equal to 1000 mg / kg, the impurity content in the lithium salt product is significantly reduced and it is easier to separate from the lithium fluoride. This is because when lithium fluoride has this size and a low carbonate content, it competes with the carbonate for reaction. The lithium fluoride participates in the reaction rapidly and completes the reaction in a short time. Therefore, the impurity content is not only lower, but the lithium salt product and impurities do not form an encapsulation relationship. Even if a small amount of impurities are generated in the system, because the amount of impurities is very small and they are independent of the lithium salt product, removal is easier.

[0026] In one specific embodiment, the purity of lithium fluoride is greater than 99.8%. When the purity of lithium fluoride is within the above range, the content of impurities such as carbonates in the lithium fluoride is low, and correspondingly, the impurity content in the lithium salt product prepared from this lithium fluoride is also low, thereby greatly improving the performance of the lithium salt product and significantly enhancing the stability of the electrolyte and the performance of the battery. Further, the purity of lithium fluoride is greater than 99.9%.

[0027] The inventors discovered that when the particle size of lithium fluoride meets the above requirements, as the mass content of carbonate in lithium fluoride decreases within a certain range, the impurity content in lithium salt products shows a decreasing trend. In particular, when the mass percentage of carbonate in lithium fluoride is less than or equal to 600 mg / kg, the storage performance of lithium salt products prepared from lithium fluoride is even better.

[0028] Furthermore, when the D10 of lithium fluoride is less than or equal to 7 μm and the D50 is less than or equal to 15 μm, impurities in lithium fluoride are more easily removed, thereby further improving the purity of lithium fluoride. For example, the D10 of lithium fluoride is 0.5 μm, 1 μm, 2 μm, 3 μm, 3.5 μm, 4 μm, 4.6 μm, 5 μm, 6 μm, 6.1 μm, 7 μm, or any range between two of these; the D50 of lithium fluoride is 5 μm, 5.7 μm, 6 μm, 7 μm, 8.5 μm, 10 μm, 11.5 μm, 12 μm, 14 μm, 14.3 μm, 15 μm, or any range between two of these.

[0029] While reducing the carbonate content and decreasing the D10 and D50 of lithium fluoride can improve its performance, the inventors found that as the carbonate content, D10, and D50 decrease within a certain range, the impurity content in the lithium salt product initially decreases but then remains relatively constant. Furthermore, further reducing the carbonate content, D10, and D50 also increases the production cost of lithium fluoride. Therefore, for economic reasons, the carbonate content is generally greater than or equal to 0.1 mg / kg, and the D10 and D50 of lithium fluoride are generally greater than or equal to 1 μm and 1 μm, respectively.

[0030] In one specific embodiment, the carbonate in lithium fluoride includes lithium carbonate.

[0031] In one specific embodiment, the lithium fluoride also contains impurities, which, by mass content, include: iron ions ≤ 5 ppm, magnesium ions ≤ 8 ppm, calcium ions ≤ 8 ppm, sodium ions ≤ 10 ppm, potassium ions ≤ 10 ppm, aluminum ions ≤ 5 ppm, chloride ions ≤ 10 ppm, and sulfate ions ≤ 10 ppm. When the content of impurity ions in the lithium fluoride is within the above range, the lithium fluoride has higher purity, thereby enabling the lithium salt product prepared from this lithium fluoride to have higher purity, further avoiding the probability of other side reactions in subsequent battery applications that lead to a decrease in battery performance.

[0032] In one specific embodiment, the water content in the lithium fluoride is less than 500 mg / kg. When the water content in the lithium fluoride is within the above range, the product prepared using this lithium fluoride as a reactant can be used in the electrolyte to reduce the water content in the electrolyte and avoid the deterioration of the battery's electrochemical performance caused by the accelerated decomposition of the electrolyte.

[0033] Currently, most commercially available lithium fluoride is produced by carbonizing lithium carbonate with carbon dioxide to obtain lithium bicarbonate, followed by fluorination of the lithium bicarbonate with hydrofluoric acid or ammonium fluoride to obtain lithium fluoride. However, this method suffers from a high residual lithium carbonate content, resulting in a high lithium carbonate content in commercially available lithium fluoride. Furthermore, commercially available lithium fluoride is typically dried using a conventional heating method, leading to a larger particle size, which is detrimental to its subsequent applications. Therefore, in order to prepare lithium fluoride with the aforementioned carbonate content and size specifications, this application provides a method for preparing lithium fluoride, comprising the following steps:

[0034] 1) Mix lithium carbonate with water and pulp to form a lithium carbonate slurry with a mass percentage of 10-30%;

[0035] 2) Add hydrofluoric acid to the lithium carbonate slurry and react the system at a pH of 3-6 until the pH of the reaction system does not change, to obtain the reactant. The reactant is then microwave dried to obtain lithium fluoride.

[0036] The reaction temperature is 10-70℃; preferably, the reaction temperature is 30-60℃.

[0037] Specifically, in step 1), lithium carbonate is mixed with water and then pulped to ensure that the lithium carbonate and water are mixed as evenly as possible, resulting in a lithium carbonate slurry. During the mixing process, the mass ratio of water to lithium carbonate is controlled to ensure that the mass percentage of lithium carbonate in the lithium carbonate slurry is 10-30%. A mass percentage below 10% will lead to a decrease in yield, while a mass percentage above 30% will result in uneven pulping, high lithium carbonate residue in the product, and difficulty in removing anions.

[0038] This application does not limit the specific method used for pulping treatment. For example, stirring treatment, ultrasonic dispersion treatment, etc. can be used, and the method can be selected according to actual needs.

[0039] Step 2): Under stirring conditions, hydrofluoric acid is slowly added to the lithium carbonate slurry to obtain a reaction system until the pH of the reaction system is 3-6. Then, the reaction is carried out at a temperature of 10-70℃, and further at 30-60℃, until the pH of the reaction system does not change, and a reaction solution is obtained. The reaction solution is then subjected to solid-liquid separation and washing to obtain the reactant. Subsequently, the reactant is subjected to microwave drying to obtain lithium fluoride.

[0040] This application does not limit the specific method of solid-liquid separation; for example, filtration, precipitation, or other methods may be selected.

[0041] The washing process in this application can use water as the detergent. In order to control the water content of the final lithium fluoride, the mass ratio of detergent to the solid phase obtained after solid-liquid separation is generally controlled to be (5-10):1.

[0042] The preparation method of this application first involves slurrying lithium carbonate with water. This process promotes a uniform reaction between lithium carbonate and hydrofluoric acid solution, avoids overly vigorous reactions that could lead to safety hazards, and prevents lithium carbonate from being encapsulated in the lithium fluoride product, resulting in excessively high lithium carbonate residues. Furthermore, maintaining a pH of 3-6 during the reaction process helps improve reaction efficiency, allowing more lithium carbonate to participate in the reaction and form lithium fluoride. A pH below 3 leads to a decrease in yield, while a pH above 6 results in an increase in the carbonate content of the product. During the reaction, hydrofluoric acid is continuously consumed, causing the pH to rise. Therefore, to maintain the pH, hydrofluoric acid needs to be continuously added to the system until the pH no longer changes, indicating that the reaction is complete.

[0043] It is worth mentioning that, because heat is transferred from the outside to the inside in traditional heating drying, the outer layer of moisture evaporates first, causing clumping and encapsulation. This not only results in high water content in lithium fluoride but also leads to larger particle size in the dried product. In contrast, microwave drying diffuses heat from the center outward, allowing moisture to evaporate more thoroughly from the inside out. Furthermore, the evaporation process produces a puffing effect, resulting in a dried product that meets the aforementioned size parameters.

[0044] Therefore, the preparation method of this application can produce carbonates with a mass content of less than 1000 mg / kg, a D10 of less than 10 μm, a D50 of less than 20 μm, and a bulk density of 0.9-1.2 g / cm³. 3 The method for producing lithium fluoride is beneficial for the subsequent applications of lithium fluoride, and it is simple in process, requires low equipment, and has high production efficiency.

[0045] It is understandable that the pulping process temperature should not be too high or too low. If the temperature is below 0°C, it will be detrimental to the dispersion of lithium carbonate; if the temperature is too high, lithium carbonate may absorb excessive water, increasing the water content. Therefore, to further ensure the effectiveness of the pulping process, the above pulping process is carried out at 10-30°C.

[0046] In one specific embodiment, the microwave frequency for microwave drying is 900-1100MHz, such as 900MHz, 920MHz, 940MHz, 960MHz, 980MHz, 1000MHz, 1020MHz, 1040MHz, 1060MHz, 1080MHz, or 1100MHz, and the microwave time is 1-2 hours, such as 1 hour, 1.1 hours, 1.2 hours, 1.3 hours, 1.4 hours, 1.5 hours, 1.6 hours, 1.7 hours, 1.8 hours, 1.9 hours, or 2 hours. When the microwave frequency and microwave time are within the above range, microwave drying can provide sufficient heat to the reactants, allowing moisture to evaporate rapidly from the inside out, producing a greater expansion effect. This results in smaller particle sizes of the dried lithium fluoride, thereby significantly improving the quality of the lithium fluoride.

[0047] In one specific embodiment, hydrofluoric acid is added to the lithium carbonate slurry dropwise over a period of 0.5-3 hours, such as 0.5 hours, 1 hour, 1.5 hours, 2 hours, 2.5 hours, or 3 hours. When hydrofluoric acid is slowly added to the lithium carbonate slurry, the lithium carbonate reacts fully with the hydrofluoric acid solution, ensuring that the lithium carbonate is reacted into lithium fluoride. This avoids an overly vigorous reaction that could lead to safety hazards, and also prevents the rapid formation of lithium fluoride from causing the lithium carbonate to be coated. This results in high-purity lithium fluoride with a low carbonate content. Furthermore, the dropwise addition time needs to be determined based on the reaction temperature in step 2). As hydrofluoric acid is added, the system temperature rises; therefore, the system temperature can be maintained between 10-70°C by controlling the dropwise addition time.

[0048] In one specific embodiment, the mass percentage of hydrofluoric acid is 30-48%, for example, 30%, 32%, 34%, 36%, 38%, 40%, 42%, 44%, 46%, or 48%. When the mass percentage of hydrofluoric acid is within the above range, it can fully react with lithium carbonate to generate lithium fluoride, and the reaction rate is suitable, avoiding violent reactions, thereby obtaining lithium fluoride with high purity and low carbonate content. Furthermore, while ensuring safety, it also minimizes the water content in the system, effectively suppressing the generation of impurities in the lithium salt product.

[0049] In one specific embodiment, the lithium carbonate is high-purity lithium carbonate, and the impurities in the high-purity lithium carbonate, by mass percentage, include: iron ions ≤ 8 ppm, magnesium ions ≤ 12 ppm, calcium ions ≤ 11 ppm, sodium ions ≤ 14 ppm, potassium ions ≤ 14 ppm, aluminum ions ≤ 7 ppm, sulfate ions ≤ 80 ppm, and chloride ions ≤ 80 ppm. When high-purity lithium carbonate with the above-mentioned impurity content is used as a raw material for the preparation of lithium fluoride, the low impurity content in the high-purity lithium carbonate results in a low impurity content introduced during the preparation of lithium fluoride, which is beneficial for obtaining high-purity lithium fluoride. Furthermore, it can avoid side reactions caused by impurities during the preparation of lithium fluoride, preventing the formation of other by-products and further improving the purity of lithium fluoride.

[0050] In one specific embodiment, the pulping process includes the following steps:

[0051] The total mass of lithium carbonate is divided into N parts, where the set of N is denoted as S = {1,2,…,i-1,i,…,N};

[0052] With mass m i The i-th part of lithium carbonate and mass M i The water is mixed and stirred at a speed of V. i The pulping process is carried out until the viscosity is ≤2mPa·s to obtain the i-th system;

[0053] Let the i-th system have a mass of m. i+1 The (i+1)th portion of lithium carbonate and mass M i+1 Water is mixed and stirred at a speed of V. i+1 The pulping process is carried out until the viscosity is ≤2mPa·s to obtain the (i+1)th system.

[0054] The pulping process is carried out sequentially until all the lithium carbonate is mixed with all the water to form the lithium carbonate slurry, and the mass percentage of lithium carbonate in each system is ensured to be 10-30%.

[0055] Specifically, lithium carbonate is divided into N parts (N≥2), and the ratio of lithium carbonate in each part to the total lithium carbonate is controlled (m i / m) is in the range of 0-1, and then the i-th part of lithium carbonate (mass m) is added. i ) and water (mass M) i Mix at a stirring speed V i The mixture is pulped until the viscosity is ≤2 mPa·s to obtain the i-th system; then the i-th system and the (i+1)-th portion of lithium carbonate (mass m) are mixed. i+1 ) and water (mass M) i+1 Mix at a stirring speed V i+1Perform pulping treatment until the viscosity is ≤2 mPa·s to obtain the (i+1)th system; repeat the above operation until the Nth system is obtained, and control m i / m i+1 The ratio is in the range of 1-10, M i / M i+1 The ratio is in the range of 1-10, V i / V i+1 The ratio is in the range of 0.5-2.

[0056] The value of N can be adjusted according to the actual situation. For example, N can be selected from 2, 3, 4, 5 or 6.

[0057] If lithium carbonate agglomerates during the pulping process, the lithium carbonate inside the agglomerates will have difficulty reacting with hydrogen fluoride. This leads to the lithium carbonate on the outside of the agglomerates reacting with hydrogen fluoride to form lithium fluoride, resulting in lithium fluoride containing lithium carbonate. Therefore, to further reduce the lithium carbonate content in lithium fluoride, this application employs a multi-stage pulping process. This allows for thorough mixing of lithium carbonate and water, preventing agglomeration and ultimately achieving the preparation of high-purity lithium fluoride with low lithium carbonate content.

[0058] In one specific embodiment, the pulping process includes the following steps: dividing lithium carbonate of total mass m into three parts, wherein 1 / 2 ≤ m1 / m < 1, 0 < m2 / m ≤ 1 / 3, and 0 < m3 / m ≤ 1 / 6; mixing the first part of lithium carbonate of mass m1 with water of mass M1, and pulping at a stirring speed V1 until the viscosity is ≤ 1.6 mPa·s, to obtain a first system; mixing the first system, the second part of lithium carbonate of mass m2, and water of mass M2, and pulping at a stirring speed V1... The mixture is stirred at a speed of V2 until the viscosity is ≤1.6 mPa·s to obtain the second system. The second system, a third portion of lithium carbonate with a mass of m3, and water with a mass of M3 are mixed and stirred at a speed of V3 until the viscosity is ≤1.6 mPa·s to obtain the third system. Wherein, 1≤m1 / m2≤4, 1≤m2 / m3≤3, 1≤M1 / M2≤4, 1≤M2 / M3≤3, 0.5≤V1 / V2≤1, 0.5≤V2 / V3≤1.

[0059] Specifically, lithium carbonate is divided into three parts: the first part has a mass of m1, the second part has a mass of m2, and the third part has a mass of m3. The following parameters are controlled: 1 / 2 ≤ m1 / m < 1, 0 < m2 / m ≤ 1 / 3, 0 < m3 / m ≤ 1 / 6, 1 ≤ m1 / m2 ≤ 4, and 1 ≤ m2 / m3 ≤ 3. The first part of lithium carbonate is then mixed with water of mass M1 and pulped at a stirring rate of V1 until the viscosity is ≤ 1.6 mPa·s, resulting in the first system. The first system, the second part of lithium carbonate, and the third part of lithium carbonate are then mixed with water of mass M2 and pulped at a stirring rate of V2 until the viscosity is ≤ 1.6 mPa·s, resulting in the second system. The second system, the third part of lithium carbonate, and the third part of lithium carbonate are then mixed with water of mass M3 and pulped at a stirring rate of V3, resulting in the third system. The following parameters are controlled: 1 ≤ M1 / M2 ≤ 4, 1 ≤ M2 / M3 ≤ 3, 0.5 ≤ V1 / V2 ≤ 1, and 0.5 ≤ V2 / V3 ≤ 1.

[0060] This application divides the pulping process into three steps and controls the pulping parameters within the above-mentioned range, which can make the lithium carbonate slurry more uniform, which is conducive to uniform reaction with hydrofluoric acid solution, avoid safety hazards, and can further prevent lithium carbonate from being encapsulated in lithium fluoride products, resulting in excessive lithium carbonate residue, and further improve the purity of lithium fluoride.

[0061] In one specific embodiment, step 2) further includes the following step after the reaction continues until the pH of the reaction system remains unchanged: adjusting the pH of the reaction system to 7-10. When the reaction continues until the pH remains unchanged, hydrofluoric acid may remain in the reaction system, making the system acidic. Lithium fluoride has higher solubility under acidic conditions. Therefore, adjusting the pH of the reaction system to 7-10 reduces the solubility of lithium fluoride, thereby increasing the yield of lithium fluoride and avoiding waste.

[0062] This application does not limit the raw materials used to adjust the pH of the reaction system to 7-10. They can be selected according to actual needs. For example, lithium hydroxide solution can be used to avoid the introduction of other impurity ions.

[0063] This application also provides a lithium fluoride prepared by the above method, wherein the mass content of carbonate in the lithium fluoride is less than or equal to 1000 mg / kg; the lithium fluoride has a D10 of less than or equal to 10 μm, a D50 of less than or equal to 20 μm, and a bulk density of 0.9-1.2 g / cm³. 3 .

[0064] Using lithium fluoride as a raw material for preparing lithium salt products can significantly reduce the impurity content in lithium salt products, thereby improving the stability of the electrolyte, inhibiting precipitation during storage and application, and helping to improve the cycle performance of lithium-ion batteries.

[0065] This application also provides lithium hexafluorophosphate, which is prepared from a raw material system including the aforementioned lithium fluoride. Specifically, it is prepared by reacting lithium fluoride with phosphorus pentafluoride gas under an inert atmosphere.

[0066] In one specific embodiment, lithium fluoride is mixed with anhydrous hydrogen fluoride, and the mixed solution is reacted with phosphorus pentafluoride at -20 to -5°C to obtain the solution.

[0067] In another specific embodiment, lithium fluoride is mixed with an organic solvent, and the mixture is then refluxed with phosphorus pentafluoride to obtain the product. Examples of organic solvents include ethylene carbonate, diethyl carbonate, and dimethyl carbonate.

[0068] Due to its specific size and low carbonate content, lithium fluoride can rapidly participate in the reaction to form lithium hexafluorophosphate (LiPF6). This not only improves the purity of LiPF6 but also reduces the difficulty of separating it from impurities. Applying LiPF6 to electrolytes results in higher electrolyte storage stability and ensures high electrochemical performance of the battery.

[0069] This application also provides a lithium bis(fluorosulfonyl)imide, which is prepared from a raw material system including the aforementioned lithium fluoride. Specifically, it is prepared under an inert atmosphere using lithium fluoride as a raw material under solvent-free conditions.

[0070] In one specific embodiment, lithium fluoride is mixed with difluorosulfonylimide and reacted at 100-140°C to obtain the product.

[0071] Similarly, due to the specific size and low carbonate content of lithium fluoride, the lithium bis(fluorosulfonyl)imide of this application also exhibits higher quality. Applying this lithium bis(fluorosulfonyl)imide to the electrolyte results in higher electrolyte storage stability and ensures excellent battery cycle performance.

[0072] The present application will be further described in detail below through specific embodiments.

[0073] Example 1

[0074] The method for preparing lithium fluoride provided in this embodiment includes the following steps:

[0075] 1) At 30°C, lithium carbonate was mixed with water and pulped to form a lithium carbonate slurry with a mass percentage of 20%; the impurity composition of lithium carbonate is shown in Table 1A.

[0076] 2) Add a 48% hydrofluoric acid solution to the lithium carbonate slurry, and add it dropwise over 2 hours. Control the reaction at pH 5 and temperature T 70°C. When the pH no longer changes, microwave dry the reactants to obtain lithium fluoride. The microwave drying frequency is 1000 MHz and the time is 1.5 hours.

[0077] Table 1A

[0078] Example 2

[0079] The method for preparing lithium fluoride provided in this embodiment includes the following steps:

[0080] 1) At 20°C, lithium carbonate was mixed with water and pulped to form a lithium carbonate slurry with a mass percentage of 10%; the impurity composition of lithium carbonate is shown in Table 1A.

[0081] 2) Add a 48% hydrofluoric acid solution to the lithium carbonate slurry, and add it dropwise over 3 hours. Control the reaction at pH 3 and temperature T 10°C. When the pH no longer changes, microwave dry the reactants to obtain lithium fluoride. The microwave drying process is performed at a frequency of 900 Hz for 1.5 hours.

[0082] Example 3

[0083] 1) At 26℃, lithium carbonate was mixed with water and pulped to form a lithium carbonate slurry with a mass percentage of 30%; the impurity composition of lithium carbonate is shown in Table 1A.

[0084] 2) Add a 40% hydrofluoric acid solution to the lithium carbonate slurry, and add it dropwise for 1 hour. Control the reaction at pH 4 and temperature T 40°C. When the pH no longer changes, microwave dry the reactants to obtain lithium fluoride. The microwave drying frequency is 1100 Hz and the time is 2 hours.

[0085] Example 4

[0086] 1) At 10℃, lithium carbonate was mixed with water and pulped to form a lithium carbonate slurry with a mass percentage of 30%; the impurity composition of lithium carbonate is shown in Table 1A.

[0087] 2) Add a 48% hydrofluoric acid solution to the lithium carbonate slurry, with a dropwise addition time of 0.5 h. Control the reaction system at pH 6 and temperature T 30 °C. When the pH no longer changes, microwave dry the reactants to obtain lithium fluoride. The microwave drying frequency is 900 Hz and the time is 2 h.

[0088] Example 5

[0089] The preparation method of this embodiment is basically the same as that of Example 1. The difference is that the impurity composition of lithium carbonate in this embodiment is shown in Table 1B.

[0090] Table 1B

[0091] Example 6

[0092] The preparation method of this embodiment is basically the same as that of Example 1. The difference is that the impurity composition of lithium carbonate in this embodiment is shown in Table 1C.

[0093] Table 1C

[0094] Example 7

[0095] The preparation method of this embodiment is basically the same as that of Example 1. The difference is that the impurity composition of lithium carbonate in this embodiment is shown in Table 1D.

[0096] Table 1D

[0097] Example 8

[0098] The preparation method of this embodiment is basically the same as that of Example 1. The difference is that the impurity composition of lithium carbonate in this embodiment is shown in Table 1E.

[0099] Table 1E

[0100] Example 9

[0101] The preparation method of this embodiment is basically the same as that of Example 1. The difference is that the impurity composition of lithium carbonate in this embodiment is shown in Table 1F.

[0102] Table 1F

[0103] Example 10

[0104] The preparation method in this embodiment is basically the same as that in Example 1, except that the reaction temperature in this embodiment is 60°C.

[0105] Example 11

[0106] The preparation method in this embodiment is basically the same as that in Example 1, except that the microwave drying frequency in this embodiment is 700MHz.

[0107] Example 12

[0108] The preparation method in this embodiment is basically the same as that in Example 1, except that the pulping temperature in this embodiment is 5°C.

[0109] Examples 13-22

[0110] The preparation method of lithium fluoride provided in Examples 13-22 is basically the same as that in Example 1, except that step 1) is a multi-stage pulping process, which includes the following steps:

[0111] 1) Divide the lithium carbonate of mass m in Example 1 into three parts, wherein the mass of the first part of lithium carbonate is m1, the mass of the second part of lithium carbonate is m2, and the mass of the third part of lithium carbonate is m3.

[0112] The first part of lithium carbonate is mixed with water of mass M1 and stirred at a stirring speed V1 until the viscosity is μ1 (mPa·s) to obtain the first system.

[0113] The first system and the second part of lithium carbonate were mixed with water of mass M2 and stirred at a stirring speed V2 until the viscosity was μ2 (mPa·s) to obtain the second system.

[0114] The first system and the third part of lithium carbonate were mixed with water of mass M3 and stirred at a stirring speed V3 until the viscosity was μ3 (mPa·s) to obtain lithium carbonate slurry.

[0115] See Table 2 for specific parameters.

[0116] Table 2

[0117] Comparative Example 1

[0118] The preparation method of Comparative Example 1 is basically the same as that of Example 1, except that step 1) pulping is not performed in this comparative example.

[0119] Comparative Example 2

[0120] The preparation method of Comparative Example 2 is basically the same as that of Example 1, except that the mass percentage of lithium carbonate slurry in step 1) of the pulping treatment in this Comparative Example is 40%.

[0121] Comparative Example 3

[0122] The preparation method of Comparative Example 3 is basically the same as that of Example 1, except that the reaction temperature of step 2) in Comparative Example 3 is 100°C.

[0123] Comparative Example 4

[0124] The preparation method of Comparative Example 4 is basically the same as that of Example 1, except that step 2) of this Comparative Example is carried out under the condition of pH 7.

[0125] Comparative Example 5

[0126] The preparation method of Comparative Example 5 is basically the same as that of Example 1, except that the reaction temperature of step 2) in Comparative Example 5 is 0°C.

[0127] Comparative Example 6

[0128] The preparation method of Comparative Example 6 is basically the same as that of Example 1. The difference is that in step 2), the reactants are not dried by microwave, but dried in a regular oven at 105°C for 6 hours.

[0129] Experimental Example 1

[0130] The purity, impurity content, particle size, and bulk density of lithium fluoride in the examples and comparative examples were tested, and the results are shown in Tables 2A and 2B.

[0131] The lithium carbonate content was determined by acid-base titration; anions such as sulfate and chloride were determined by ion chromatography; cations such as iron, magnesium, calcium, sodium, potassium, and aluminum were determined by ICP-OES inductively coupled plasma atomic emission spectrometry; the moisture content was determined by drying; the lithium fluoride purity was obtained by the formula: purity = 100% - lithium carbonate content - anionic impurity content - cationic impurity content - moisture content; the particle size was determined by a particle size analyzer; and the bulk density was determined according to GB / T 3603.

[0132] Table 2A

[0133] Table 2B

[0134] Experimental Example 2

[0135] The lithium hexafluorophosphate was prepared from the lithium fluoride obtained in Examples 1-4, 10-22 and Comparative Examples 1-6, including the following steps:

[0136] Under a nitrogen atmosphere, lithium fluoride was mixed with ethylene carbonate solvent, and the mixed solution was reacted with phosphorus pentafluoride at -20°C for 30 min to obtain a lithium hexafluorophosphate ethylene carbonate solution, which was then concentrated to a suitable concentration for later use. The molar ratio of lithium fluoride to phosphorus pentafluoride was 1:1. The acidity and insoluble matter of this lithium hexafluorophosphate product were tested according to the method for lithium hexafluorophosphate concentrate (Q / TC 049-2023), and the test results are shown in Table 3A below.

[0137] The above-mentioned lithium hexafluorophosphate ethylene carbonate solution was used as an electrolyte. The electrolyte preparation method included the following steps: In an argon-filled glove box (H2O < 0.1 ppm, O2 < 0.1 ppm), PC / DEC / PP were mixed evenly at a mass ratio of 20 / 40 / 30 and then mixed with the lithium hexafluorophosphate ethylene carbonate solution. The mixture was stirred evenly to form an electrolyte with an EC / PC / DEC / PP mass ratio of 10 / 20 / 40 / 30, and lithium hexafluorophosphate accounting for 14% of the total mass. The storage stability of this electrolyte at 25°C (acidity and color were tested on days 0, 7, 15, and 30) was tested according to the method for electrolytes for lithium-ion batteries in Q / TC 060-2024. The results are shown in Table 3B.

[0138] Acidity testing method: Utilizing the principle of acid-base neutralization titration, the titration endpoint is determined by the color change of an indicator, thus achieving the purpose of measurement. Add 50 mL of acetone reagent to a beaker, add 3-5 drops of bromophenol blue ethanol indicator and a magnetic oscillator, and adjust the rotation speed to 500 rpm (at this point, the solution is slightly yellow or colorless); add 5-8 g of sample using the decreasing method, and rapidly titrate with 0.01 mol / L triethylamine / EMC standard solution using an electronic titrator until the solution gradually turns yellow, then titrate until a localized blue color appears, reduce the titration speed, and slowly titrate until the solution is completely blue, which is the endpoint, and maintain the color for 3-5 seconds without fading, which is the titration endpoint; record the volume (mL) of triethylamine / EMC standard solution consumed to two decimal places; weigh the disposable syringe and calculate the sample weight. The free acid w of the sample, expressed in ppm, is calculated using the formula:

[0139] In the formula:

[0140] V—The numerical value of the volume of triethylamine / EMC standard titration solution consumed by the titration test solution, in milliliters (mL);

[0141] The accurate value of the concentration of c-triethylamine / EMC standard titration solution, in moles per liter (mol / L);

[0142] m—the numerical value of the sample mass, in grams (g);

[0143] M—The numerical value of the molar mass of hydrofluoric acid (HF), in grams per mole (g / mol) (M = 20.01).

[0144] The test results are the average of two parallel samples, and the results are rounded to 0.1 mg / kg. The ratio of the absolute difference between the two parallel determinations to the arithmetic mean is no greater than 20%.

[0145] Method for detecting insoluble matter: Take a weighing bottle and a filter membrane that have been dried to constant mass at 105℃±2℃. Accurately weigh the filter membrane as m1, with a mass accurate to 0.0001g. Weigh an appropriate amount of sample using the subtraction method, accurate to 0.01g, and place it in a 500mL beaker. Filter the sample using a membrane filtration device. Wash the beaker three times with 100mL of a mild solvent and the filtration device five times.

[0146] Carefully remove the filter membrane and place it in a weighing bottle. Place the bottle in a drying oven and dry for 2 hours. After drying, remove the sample and cool it to room temperature in a desiccator. Weigh the dried filter membrane (m2).

[0147] The insoluble matter content is expressed as a mass fraction w, in mg / kg, and is calculated using the following formula:

[0148] In the formula:

[0149] m1 — Mass of the filter membrane before filtration, in grams;

[0150] m2 — Mass of the filter membrane after filtration and drying, in grams;

[0151] m — the mass of the sample, in grams.

[0152] The arithmetic mean of the parallel measurement results is taken as the measurement result, and the absolute difference between the two parallel results and the arithmetic mean shall not exceed 20%.

[0153] Colorimetric detection method: The liquid colorimeter uses a halogen lamp as the light source and a microprocessor to control the grating. The color test wavelength is 380nm-720nm, and the wavelength step is 10nm / step. After switching to the required setting, the specified light is shone on the sample to be analyzed and the colorless distilled water test tube respectively. After passing through the liquid, different absorption values ​​are produced, and the color value is calculated by the microprocessor.

[0154] Table 3A

[0155] Table 3B

[0156] Experimental Example 3

[0157] The lithium fluoride prepared in Examples 1-4, 10-22 and Comparative Examples 1-6 was used to prepare lithium bis(fluorosulfonyl)imide, including the following steps:

[0158] Under a nitrogen atmosphere, bis(fluorosulfonyl)imide and lithium fluoride were reacted at a molar ratio of 1:1 at 120°C. After 12 hours, the reaction solution was subjected to a devolatilization treatment at a vacuum of 0.5 kPa, a temperature of 60°C, and a time of 48 hours to obtain lithium bis(fluorosulfonyl)imide. The prepared lithium bis(fluorosulfonyl)imide was tested using the method for high-purity lithium bis(fluorosulfonyl)imide (Q / TC 054-2023) to determine its color, moisture content, acidity, and anionic impurities. The results are shown in Table 4A.

[0159] The lithium bisfluorosulfonylimide was used in the electrolyte. The electrolyte preparation method included the following steps: In an argon-filled glove box (H2O < 0.1 ppm, O2 < 0.1 ppm), EC / PC / DEC / PP were mixed uniformly at a mass ratio of 10 / 20 / 40 / 30. Then, fully dried lithium bisfluorosulfonylimide, accounting for 14% of the total electrolyte mass, was quickly added and stirred uniformly to obtain the lithium bisfluorosulfonylimide electrolyte. The storage stability of this electrolyte at 25°C (acidity and color on days 0, 7, 15, and 30) was tested according to the method for electrolytes for lithium-ion batteries in Q / TC 060-2024. The results are shown in Table 4B.

[0160] The testing methods for color and acidity are the same as in Experiment 2, while the testing methods for moisture and anionic impurities are as follows:

[0161] Moisture detection method: A Karl Fischer moisture analyzer is used for testing. Any moisture present in the sample (free water or water of crystallization) reacts quantitatively with a Karl Fischer reagent (a solution composed of iodine, sulfur dioxide, pyridine, and methanol) of known titration value. Weigh approximately 1g of sample using the subtraction method, accurate to 0.001g. After the instrument drift value drops to the set value, the "COND" light on the panel illuminates, indicating that the instrument has stabilized and the titration cell has met the required dryness for the determination. Press the "START" button to begin, quickly inject the sample, enter the sample volume, and press "ENTER" to confirm. The instrument will then enter sample measurement mode. After the sample measurement is completed, the instrument automatically stops and records the results. The instrument automatically reads the result, and the arithmetic mean of parallel measurements is taken as the final result. The ratio of the absolute difference between two parallel measurements to the arithmetic mean should not exceed 20%.

[0162] Anionic impurity detection method: Ion chromatography is used for testing. The sample is diluted to a certain concentration, with ion exchange resin as the stationary phase and the eluent as the mobile phase. Separation is achieved by the difference in affinity of chloride ions, sulfate ions, etc., in the test solution for the stationary phase. A conductivity detector converts the chemical signal of the analyte into an electrical signal. Quantitative analysis is performed using the standard curve method or the single-point external standard method.

[0163] Table 4A

[0164] Table 4B

[0165] In summary, the lithium fluoride used in this application as a raw material helps to improve the purity of lithium hexafluorophosphate and lithium bis(fluorosulfonyl)imide, thereby improving the storage stability of electrolytes containing lithium hexafluorophosphate or lithium bis(fluorosulfonyl)imide.

[0166] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application.

Claims

1. A lithium fluoride, wherein, The mass content of carbonate in the lithium fluoride is less than or equal to 1000 mg / kg; The lithium fluoride has a D10 of less than or equal to 10 μm, a D50 of less than or equal to 20 μm, and a bulk density of 0.9-1.2 g / cm³. 3 .

2. The lithium fluoride according to claim 1, wherein, The lithium fluoride has a purity greater than 99.8%, preferably greater than 99.9%.

3. The lithium fluoride according to claim 1 or 2, wherein, The mass content of the carbonate is less than or equal to 600 mg / kg; and / or, The lithium fluoride has a D10 of less than or equal to 7 μm and a D50 of less than or equal to 15 μm. The carbonate content is greater than or equal to 0.1 mg / kg; and / or, The lithium fluoride has a D10 greater than or equal to 1 μm and a D50 greater than or equal to 1 μm.

4. The lithium fluoride according to any one of claims 1-3, wherein, The carbonates include lithium carbonate.

5. The lithium fluoride according to any one of claims 1-4, wherein, The lithium fluoride also includes impurities, wherein: iron ions ≤ 5 ppm, magnesium ions ≤ 8 ppm, calcium ions ≤ 8 ppm, sodium ions ≤ 10 ppm, potassium ions ≤ 10 ppm, aluminum ions ≤ 5 ppm, chloride ions ≤ 10 ppm, and sulfate ions ≤ 10 ppm.

6. The lithium fluoride according to any one of claims 1-5, wherein, The water content in the lithium fluoride is less than 500 mg / kg.

7. A method for preparing lithium fluoride, comprising the following steps: 1) Mix lithium carbonate with water and pulp to form a lithium carbonate slurry with a mass percentage of 10-30%; 2) Add hydrofluoric acid to the lithium carbonate slurry and react the system at a pH of 3-6 until the pH of the reaction system does not change, to obtain the reactant. Then, microwave dry the reactant to obtain the lithium fluoride. The reaction temperature is 10-70℃; preferably, the reaction temperature is 30-60℃.

8. The preparation method according to claim 7, wherein, The pulping process is carried out at a temperature of 10-30℃.

9. The method for preparing lithium fluoride according to claim 7 or 8, wherein, The microwave drying process uses a microwave frequency of 900-1100MHz and a microwave duration of 1-2 hours.

10. The method for preparing lithium fluoride according to any one of claims 7-9, wherein, The hydrofluoric acid is added to the lithium carbonate slurry by dripping for 0.5-3 hours; and / or the mass percentage of the hydrofluoric acid is 30-48%.

11. The method for preparing lithium fluoride according to any one of claims 7-10, wherein, The lithium carbonate is high-purity lithium carbonate, and the impurities in the high-purity lithium carbonate include, by mass percentage: iron ions ≤ 8 ppm, magnesium ions ≤ 12 ppm, calcium ions ≤ 11 ppm, sodium ions ≤ 14 ppm, potassium ions ≤ 14 ppm, aluminum ions ≤ 7 ppm, sulfate ions ≤ 80 ppm, and chloride ions ≤ 80 ppm.

12. The method for preparing lithium fluoride according to any one of claims 7-11, wherein, The pulping process includes the following steps: The total mass of lithium carbonate is divided into N parts, where the set of N is denoted as S = {1,2,…,i-1,i,…,N}; With mass m i The i-th part of lithium carbonate and mass M i The water is mixed and stirred at a speed of V. i The pulping process is carried out until the viscosity is ≤2mPa·s to obtain the i-th system; Let the i-th system have a mass of m. i+1 The (i+1)th portion of lithium carbonate and mass M i+1 Water is mixed and stirred at a speed of V. i+1 The pulping process is carried out until the viscosity is ≤2mPa·s to obtain the (i+1)th system. Where, 0 < m i / m<1,1≤m i / m i+1 ≤10, 1≤M i / M i+1 ≤10, 0.5≤V i / V i+1 ≤2, i<N, and N≥2; The pulping process is carried out sequentially until all the lithium carbonate is mixed with all the water to form the lithium carbonate slurry.

13. The method for preparing lithium fluoride according to claim 12, wherein, The pulping process includes the following steps: Lithium carbonate of total mass m is divided into three parts, where 1 / 2 ≤ m1 / m < 1, 0 < m2 / m ≤ 1 / 3, and 0 < m3 / m ≤ 1 / 6. The first part of lithium carbonate with a mass of m1 is mixed with water with a mass of M1 and stirred at a stirring speed of V1 until the viscosity is ≤1.6mPa·s to obtain the first system. The first system, the second part of lithium carbonate with a mass of m2, and water with a mass of M2 are mixed and stirred at a stirring speed of V2 until the viscosity is ≤1.6mPa·s to obtain the second system. The second system, the third part of lithium carbonate with a mass of m3, and water with a mass of M3 are mixed and stirred at a stirring speed of V3 until the viscosity is ≤1.6mPa·s to obtain lithium carbonate slurry; Wherein, 1≤m1 / m2≤4, 1≤m2 / m3≤3, 1≤M1 / M2≤4, 1≤M2 / M3≤3, 0.5≤V1 / V2≤1, 0.5≤V2 / V3≤1.

14. The method for preparing lithium fluoride according to any one of claims 7-13, wherein, Step 2) further includes the following steps after the reaction continues until the pH of the reaction system remains unchanged: Adjust the pH of the reaction system to 7-10.

15. A lithium fluoride prepared by the method of any one of claims 7-14, wherein, The mass content of carbonate in the lithium fluoride is less than or equal to 1000 mg / kg; The lithium fluoride has a D10 of less than or equal to 10 μm, a D50 of less than or equal to 20 μm, and a bulk density of 0.9-1.2 g / cm³. 3 .

16. A lithium hexafluorophosphate, wherein, In an inert gas atmosphere, lithium fluoride as described in any one of claims 1-6 or 15 is reacted with phosphorus pentafluoride gas to obtain lithium hexafluorophosphate.

17. A lithium difluorosulfonylimide, wherein, It is prepared using lithium fluoride as described in any one of claims 1-6 or 15 as a raw material under solvent-free conditions.

18. The lithium bisfluorosulfimide of claim 17, wherein, The lithium fluoride is reacted with bis(fluorosulfonyl)imide in an inert gas atmosphere at 100-140°C to obtain the lithium(fluorosulfonyl)imide.

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